Influência de parâmetros microestruturais no comportamento tribológico de ligas ferrosas multicomponentes

Abstract

The aim of this work is to evaluate the effect of microstructural parameters (eutectic carbides and matrix hardness) of multi-component ferrous alloys on tribological behavior in sliding wear and micro-abrasive wear. The samples were two series of alloys with variable vanadium (V serie) and molybdenum (M serie) contents and fixed amounts of other elements. Each series includes an alloy free of carbides (matrix alloy) and alloys containing carbides (carbide rich alloys). Heat treatments of quenching and tempering were performed to obtain three different levels of metallic matrix hardness. The wear configuration was ball on plane reciprocating sliding tests. Load, speed and temperature were fixed. The apparent friction coeficient and wear rate were measured. Microabrasion wear test used free ballcratering with silica fine abrasives. The wear mechanisms of the types of tests were characterized by SEM and energy-dispersive X-ray (EDX). Friction was almost invariable with volumetric fraction of carbides and nominal matrix hardness. Increasing matrix hardness in alloys of V and M series was improved their wear resistance. The influence of carbide amount in wear rate was small effect in M serie alloys. In harder of the V series alloys the presence of carbides protected the 650 HV matrix. However the increase of the amount of carbides did not altere the wear rate. The following wear mechanisms occured different intensities on several alloys: pull-out of carbides, abrasion, and formation and break-down of tribochemical layers. In microabrasion, the relationship between microstructural parameters and abrasive wear coefficient was complex and not clear. The removal of matrix material due to abrasion with fine silica particles decreased the mechanical supporting of the carbides, which caused intense fracture and their pull-out.